Natural Resources

Open File LAB/1571 - Mineral Occurrences and Metallogenesis in Eastern Labrador

C.F. Gower

St. John's, Newfoundland, November, 2010

Abstract

Geological mapping and mineral exploration have resulted in the reporting of 545 mineral occurrences in the eastern Makkovik Province and the Grenville Province in eastern Labrador. This report mentions all occurrences, in the context of grouping them according their geological setting, particularly addressing the age and nature of the host rock, and identifying commodities that show repeated mutual association. The objective of this approach is to attempt to recognize generalized metallogenic settings in the hope that this concept-based approach will assist future mineral exploration in the region.

The eastern Makkovik Province (Cape Harrison domain) is characterized by U–Mo–F–pyrite mineralization, associated with mid-Paleoproterozoic felsic volcanic rocks (correlated with the ca. 1860 Ma Aillik Group), mid- to late-Paleoproterozoic granitoid rocks (1840–1650 Ma), and pegmatite–quartz veins–minor shear zones. All mineralization is attributed to late-stage felsic magmatic activity during various events, including the introduction of hydrothermal and/or meteoric fluids.

In the Grenville Province, the earliest recognized mineralization is a Cu–(Au–Zn–Mo–U)–pyrite association found in dominantly pelitic metasedimentary gneisses, probably deposited between 1810 and 1770 Ma. In eastern Labrador, mineralization is mostly pyrite and Cu, but, in probably correlative rocks in the Ketilidian mobile belt in southern Greenland, economic Au is known and deposits are also enriched Zn. Both mildly anomalous Au and Zn have been found in places in the metasedimentary gneisses in eastern Labrador. A volcanic-exhalative, Besshi-type model is favoured for this type of mineralization.

In Labradorian (1710–1600 Ma) rocks, mineralization is classified as follows: i) Cu–(Ni–Au–Pd–Pt)–pyrite and hints of Cr–V concentrations in ultramafic and mafic rocks – an association that has features in common with that known in subduction-related intrusive complexes elsewhere, including those referred to as ‘Alaskan-type’; ii) Fe–Ti oxide mineralization in anorthositic and leucogabbronoritic rocks that may include minor Cu and Ni, and which is generally linked with late-stage residual liquids from anorthosite-norite magmas; and iii) Cu (Au–REE–F–U–Th–Zr) mineralization in intrusive and extrusive felsic volcanic rocks, for which an Olympic Dam or IOCG (Iron Ore–Copper–Gold) deposit model has appeal. This tripartite grouping is in keeping with the trimodal mafic–anorthositic–monzogranitic Labradorian magmatic association previously recognized in the eastern Grenville Province.

Indications of mineralization in post-Labradorian – pre-Grenvillian rocks in eastern Labrador are sparse, but some potential may exist for Cu–Fe oxide–pyrite mineralization in layered mafic intrusions located at the interface between Labradorian and Pinwarian (1520–1460 Ma) crustal regions, as well as for Mo mineralization in ca. 1300 Ma felsic intrusions.

The best candidates for Grenvillian-related (1090–985 Ma) mineralization are, i) nepheline in mid-Grenvillian alkali-feldspar syenite, and ii) U–Mo–F–REE–pyrite mineralization in pegmatite (although not all pegmatite is necessarily of Grenvillian age). The pegmatites carry potentially economic amazonite and muscovite in places. Modelling Grenvillian metallogenesis requires an appreciation that Grenvillian orogenesis was characterized by collisional tectonism involving older rocks and concomitant modification of earlier metallogenic environments.

Post-Grenvillian mineralization can be related to rifting (615–550 Ma) that preceded the creation of Iapetus Ocean, during which time the Long Range dykes (hosting minor Cu–pyrite mineralization), and huge quartz veins were emplaced in eastern Labrador. Apart from their potential as a silica resource, the quartz veins (and associated brittle fault brecciation) carry minor sulphide in places.

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